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We have had many calls recently about the worms eating the oak tree leaves and leaving
their nasty “debris” behind. Many residents are battling the shredded leaves and
brown droppings on a daily basis. This nuisance is causing problems in swimming pools,
pet water and feed bowls and on many decks and patios. So what is this worm and how
do you fix the problem??
The Variable Oakleaf Caterpillar (Lochmaeus (Heterocampa) manteo) is a native species that occurs in deciduous forests throughout much of eastern
North America. Although outbreaks have not been uncommon throughout much of its range,
it has been several years since I can remember an outbreak of this magnitude in Arkansas.
Larvae of this insect feed on the foliage of a large number of deciduous trees. All
species of oaks are attacked; however, white oak is generally preferred. Infestations
are commonly recorded on southern red, northern red, pin, willow, black, laurel, bur,
and post oaks. Exotic oaks, beech, basswood, paper birch, and American elm also are
attacked. Occasional hosts are walnut, black birch, hawthorn, eastern hop hornbeam,
apple, box elder, and persimmon
Trees of all sizes are attacked by this insect. The greatest amount of feeding usually
occurs in August or later; consequently, saplings or larger trees can withstand 2
or 3 consecutive years of extreme defoliation before mortality occurs. Infestations
seldom last longer than 2 years, during which time tree vigor and growth are impaired.
In severe outbreaks an occasional tree may be killed, but the major effect is unsightly
defoliation that degrades forest recreation sites.
Description and Life Cycle
The tiny spotted larvae of the variable oakleaf caterpillar at first feed gregariously
on the lower leaf surface near the expended egg shells. They usually skeletonize portions
of one to three leaves in a cluster. They also separate after the first molt and begin
to feed singly. From this point on they cease to skeletonize and consume entire portions
of the leaf. They pass through five instars prior to dropping to the soil to pupate.
At maturity the color is generally green but a fairly high percentage of individuals
may be deep pink or reddish. Mature larvae are roughly 1.5" long with a distinctive
dorsal band which is often dark red in color. The head is most often green with two
darker vertical lines which are usually black, edged with creamy white. There is also
a definite yellowish lateral line along each side of the larva at or below the spiracles
(breathing pores) which separates this species from other prominents (Heterocampa).
Mature larvae drop to the soil when done feeding, usually in late August or September.
They burrow into the soil beneath the leaf litter and form a loose silk lined cell.
Here they become inactive larvae (pre-pupae) and remain in this state throughout the
Pupation of this species usually takes place in the soil cell in late May or June
of the next year. Some individuals, however, remain prepupae throughout the entire
following season and pupate in May or June of the second spring following defoliation.
Pupae of the variable oakleaf caterpillar are about .75" long, light chestnut brown,
smooth and shiny.
One generation per year is normal in the northern areas of the variable oakleaf caterpillar's
range. In areas south of a line extending from Virginia to Missouri, two generations
have been reported. However, only one generation usually reaches outbreak population
levels in any one place each year.
The insects over winter as pre-pupae in cocoons under the leaf litter. Pupation usually
occurs the following spring; in heavy outbreaks, however, over 50 percent of the insects
may remain as pre-pupae for a second year or longer.
In the North, the moths begin to emerge near the end of June and continue to emerge
through late July. Females lay their eggs in clusters of 30 to 300 on the lower surface
of host leaves. Each female may lay as many as 500 eggs, which hatch in 5 to 7 days.
At first the young larvae feed gregariously, skeletonizing the lower surface of the
leaves. As they become older, they consume all the foliage between the major veins.
Larvae in the last stage account for about 85 percent of the defoliation.
When disturbed, larvae defend themselves by secreting formic acid from a gland on
their ventral thorax. Prolonged or repeated handling of the larvae may cause blisters.
Larvae cease feeding early in September, drop to the ground, crawl into the duff,
and spin their cocoons.
In the South, some moths may begin to emerge about mid-April or early May. Eggs are
usually present by the end of April. Larvae hatch from these eggs in May, feed until
late June or early July, and then pupate in cocoons in the leaf litter. Adult moths
appear and lay eggs by late July. Second-generation larvae begin feeding by mid-August,
paralleling the development of northern populations. Upon completion of feeding in
September, they move to the ground and spin their cocoons. This generation over winters
as pre-pupae and pupates in April of the following year.
Development varies from year to year, depending on local weather conditions or latitude.
In one instance in Arkansas, larvae were observed feeding in January.
Variable oakleaf caterpillars are frequently found feeding with one or more other
species of related Lepidoptera. Such combined feeding activity defoliates a stand
of trees more severely than feeding by the oakleaf caterpillars alone. The most commonly
associated species are the redhumped oakworm (Symmerista canicosta Fran.), the yellownecked caterpillar (Datana ministra (Drury)), the walnut caterpillar (Datana integerrima G. & R.), the saddled prominent (Heterocampa guttivitta (Wlkr.)), and the orangestriped oakworm (Anisota senatoria (J. E. Smith)). All these caterpillars belong to the variable oakleaf caterpillar
family or are close relatives and have similar life histories and habits.
In years following large infestations, the egg parasites Trichogramma sp. and Telenomus sp. may kill 90 percent of the eggs. Nearly all egg masses have some parasitized
eggs; only the eggs concealed within a cluster escape. This high level of parasitization,
plus the failure of many prepupae to pupate in the spring, appears to be the major
reasons for lack of consecutive heavy defoliations.
At least seven species of larval parasites attack variable oakleaf caterpillar larvae.
The most important species are Diradops bethunei Cress (Ichneumonidae), Protomicroplitus schizurae (Braconidae), and Lespesia schizurae (Tachinidae). Combined larval parasitization may kill 90 percent of the larvae.
The large predatory ground beetles Calosoma scrutator (F.) and C. calidum (F.) feed on the variable oakleaf caterpillar. Adult checkered beetles and stink
bugs often prey on small larvae. Most birds do not prey upon active larvae although
prepupae have been found in the crops of ruffed grouse and wild turkeys.
Most outbreaks, although spectacular, subside before tree mortality occurs. Chemical
control is generally neither necessary nor recommended over large areas. However,
localized treatments using pesticides may be necessary in residential or recreation
areas. Since most of the calls I have received are large and this outbreak is widespread,
control is most likely impractical. It looks like we will have to tolerate this nuisance
and keep the broom and pressure washer handy to clean up their manure and the shredded
Normally populations of these late season defoliators drop out after two or three
years in any one area without serious impact. Chemical control is neither necessary
nor recommended in forest stands and the most significant damage occurs where a stand
is opened up due to heavy defoliation. In this case heat and/or drought can cause
serious root damage resulting in dieback or mortality of severely stressed trees.
*NOTE:These recommendations are not a substitute for pesticide labeling. Read the label
before applying any pesticide. Pesticide recommendations are contingent on continued
EPA and Maine Board of Pesticides Control registration and are subject to change.
Caution: For your own protection and that of the environment, apply the pesticide only in
strict accordance with label directions and precautions.
By Sherri Sanders County Extension Agent - AgricultureThe Cooperative Extension ServiceU of A System Division of Agriculture
Media Contact: Sherri Sanders County Extension Agent - AgricultureU of A Division of AgricultureCooperative Extension Service411 No Spruce Searcy AR 72143 (501) 268-5394 firstname.lastname@example.org
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